During the firing of large calibre guns, the combustion gases and pressure waves generated by the blast of the gun can be considerable. As a result, especially for guns of 120 mm calibre or greater, the operator of the gun has to station himself at a safe distance from the blast area to avoid injuries that may be caused by such pressure levels. In the case of muzzle-loaded weapons, such as mortars, the problem is more acute as it is necessary for the operator to be in relatively close proximity to the barrel in order to operate the weapon effectively.
Due to a desire to increase the rate of fire of a mortar gun, the peak sound pressure level at the operator's position when firing the mortar artillery system would tend to exceed the safety limit of the “Z line zone” as defined in the military standardization specifications MIL-STD 1474C (“Noise limits for military material”). This problem has constrained the firepower of the mortar system as it limits the total number of rounds that can be safely fired per day by an operator.
Conventionally, this problem may be resolved by remotely triggering the mortar firing. However, the rate of fire will be significantly reduced. The problem is accentuated by the development of modern mortar systems that are designed for high rates of fire with semi-automatic bomb loading systems.
There are various devices that have been developed to attenuate the sound pressure levels generated by the firing of a gun. A majority of these devices seek to divert the propellant gases leaving the gun barrel so that they may be allowed to expand or cool inside a chamber, or by drawing the propellant gases out of the barrel in a controlled manner. An example is U.S. Pat. No. 5,610,360 for a “Large Caliber Gun Muffler”. The patent describes a muffler for a large calibre gun having a gun tube that includes a transition section fitted around the gun tube and engaging the gun tube for preventing the escape of residual combustion gases caused by the firing of a projectile by the gun. The transition section further includes a pressure vessel, vent stack, valve and exhaust blower to draw propellant gases out of the gun tube.
The device described in the patent is elaborate and contains many parts. It also includes external attachments such as an exhaust blower which increases the complexity of the operation. Whilst it may be workable in a gun-testing environment, it is not practical for field combat operations because of its complexity and bulk, that would add to the operational overheads.